Acoustics

Technology To Manage Pipelines
Immediately upon organization of Pipeline Technologies Inc in June 1995, the firm answered a formidable challenge of the pipeline industry to develop a method of determining the structural condition of buried large diameter water pipelines while they remain in service. PTI, parent firm of Pipetech International, conducted a rigorous development program to meet this challenge, resulting in the introduction of acoustic emission technology to the PCCP industry in late 1996. In the decade since its introduction, acoustic emission technology has become the widely used technology of choice for determining the health of PCCP pipelines on every continent throughout the world.

The system used for this testing is the highly accurate and effective Autonomous Hydrophone System (US Patent 5,987,990) The system uses hydrophones or other transducers placed along a pipe to listen passively for sounds that are made by the breaking of the pre-tensioned reinforcement wire in the pipe. By detecting the sound at two or more locations and establishing the precise time differentiation, the system calculates the location of the defect.

This technology has identified thousands of sections of PCCP that are in a state of deterioration, allowing pipeline owners to repair these sections, and extend the useful life of PCCP pipelines.

Background
Prestressed Concrete Cylinder Pipe (PCCP) was developed and used in the United States in the mid-1940’s as a means to provide an economical means of conveying water under pressure. The nature of the steel alloy used and the method of applying the steel wire to the concrete pipe core under tension, made very efficient use of the concrete and steel materials that constitute PCCP. The competitive cost of PCCP, its durability, and its anticipated long life led to increasing acceptance and use of the product. By the late 1960’s, PCCP was the preferred pipe product for large pressure water pipelines in the United States. The product is widely used in other parts of the world as well, including Europe, the Middle East, Australia, South America, North Africa, and China.

Due to a wide variety of causes, there are over five hundred recorded failures of PCCP in the world. The causes of failure may be related to improper design, manufacturing flaws, improper construction, improper operation, environmental conditions, and damage by outside agents. In many instances it is difficult to assign a specific cause to a particular pipeline, and indeed this alludes to another problem faced by pipeline owners: Regardless of the causes of pipe distress, the fact is that our assets are continuing to age, and failures will occur with increasing frequency as they become older. In the absence of tools to diagnose the condition of any asset, it is virtually impossible to maintain the asset; and its catastrophic failure may occur without warning. On the other hand, given reliable means to diagnose pending failure, and the tools to rehabilitate at these points, the asset will be maintainable. It will take on a new life, as the owner is able to manage the asset, to project maintenance costs, and achieve a maximum useful life with an increased degree of confidence.

The American Water Works Association’s recent publication “Dawn of the Replacement Era – Reinvesting in Drinking Water Infrastructure,” captures this theme with a great deal of clarity. This “buried treasure beneath our feet” – as they refer to our pipeline infrastructure – has not been well maintained, partly because they are generally reliable, partly because we can’t see them, and partly because we didn’t even pay for them initially. We would add another reason to our neglect, that before the advent of diagnostic tools it was somewhere between difficult and impossible to undertake a maintenance program. And now with the introduction acoustic tools in the toolbox, many new possibilities become apparent. PCCP maintenance is analogous to health care or automobile maintenance or other pipe materials for that matter, in several respects. Physicians and mechanics alike depend on diagnostic tools. Pipeline owners are developing the same capability. We need to develop the confidence in them before we are confident, however. Do they work??

In their search for a means of determining the condition of PCCP, Pipeline Technologies Inc had perceived that acoustic emission technology might hold promise. Early experiments had demonstrated that the prestressing wire in PCCP emits a sharp sound when it breaks. PTI had detected and recorded these sounds using underwater microphones, or hydrophones, at a distance of one mile in large diameter pipes.

Early interest in AET stemmed from operational aspects of this technology as well as its technical potential. The owner needs a pipeline inspection method which:

is reliable

is quick

performs without taking the pipeline out of service

performs without uncovering the pipeline

will detect areas of distress early enough to permit refurbishment

is cost-effective

Many technologies and methods which held promise of meeting several of these criteria but AET appeared to have the potential to meet all six.